#10892: ApplicativeDo should use *> and <* -------------------------------------+------------------------------------- Reporter: simonmar | Owner: bollu Type: task | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 7.11 Resolution: | Keywords: ApplicativeDo Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: 12143 Related Tickets: #13309 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by AaronFriel): A user ElvishJerricco on Reddit posted an interesting test case ([[https://www.reddit.com/r/haskell/comments/6c7hen/applicativedo_overhaul_request_for_comments/dhw9po0/?context=3|my analysis here]]). There were two interesting things that popped out. Here's the reduced test case: {{{#!hs {-# LANGUAGE ApplicativeDo #-} foo :: Monad f => f () -> f () foo f = f bar :: Monad f => f () -> f () bar f = do _ <- f foo f }}} Clearly the two statements of `bar` are independent, and so we should use `*>` here too. The interesting thing to me is that this doesn't trigger the `ApplicativeDo` desugaring at all! The desugarer outputs: `bar = f >>= \_ -> foo f`. So this is another thing to make sure my revised rules cover. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10892#comment:27 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler